1. Field of the Invention
The present invention relates to a meter for automobiles and more particularly to an automotive meter having a self-illuminating pointer.
2. Prior Art
A conventional automotive meter of this kind is illustrated in FIG. 9, in which a light emitting diode is used as a light source for the self-illuminating pointer. In the figure, the meter consists of: a drive unit 1 as a meter body to drive a pointer shaft 1a according to the amount of a quantity measured; a face plate 2; a light conducting member 3 arranged at the back of the face plate 2 to illuminate characters and scales printed on the face plate 2; and a pointer 4 securely fixed to the pointer shaft 1a.
The pointer 4 has an indicating portion 4a made of transparent acrylic resin which is inclined upward toward its free end at the underside 4a.sub.1 that forms a diffused reflection surface. The indicating portion 4a has its base portion securely fitted with a printed circuit card 4b. Mounted on the upper surface of the printed circuit card 4b is a light emitting diode 4c whose pair of lead terminals 4d are connected electrically and mechanically as by solder to a conducting pattern (not shown) on the card 4b. One end of a pointer collar 4e made of conductive material is secured through press fit into the center hole of the printed circuit card 4b. The pointer collar 4e is electrically connected to the conducting pattern on the printed circuit card 4b to which one of the lead terminals 4d of the light emitting diode 4c is connected. The pointer collar 4e has a through-hole 4e.sub.1 passing therethrough, into which the end of the pointer shaft 1a is pressed.
The drive unit 1 is mounted to the back of the light conducting member 3 by screws 1d at two mounting pieces 1b, 1c so that the pointer shaft 1a is situated at the center of an opening 2a of the face plate 2 and of an opening 3a of the light conducting member 3. At the base of the mounting pieces 1b, 1c a first terminal 1e and a second terminal 1f are attached. The pointer shaft 1a is securely fitted with a connector block 1h made of conductive material which connects the inner end of a hair spring 1g to the pointer shaft 1a. The hair spring 1g is made of phosphor bronze and acts to reset the pointer 4 to a zero position on the face plate 2. The outer end of the hair spring 1g is fixed to the first terminal 1e.
The pointer shaft 1a is also fitted under pressure insulating seat 1i formed of insulating material. The insulating seat 1i has a through-hole 1i.sub.1 at the center and a large-diameter flange 1i.sub.2 formed at the bottom. The through-hole 1i.sub.1 consists of: a small diameter hollow portion into which the pointer shaft 1a is press-fitted; and a large-diameter hollow portion into which a large-diameter portion on a part of the outer circumference of the pointer collar 4e is fitted. Fixed to the outer circumference of the insulating seat 1i is a connector block 1k made of conductive material which connects the inner end of a hair spring Ij to the insulating seat 1i. The outer end of the hair spring 1j is secured to the second terminal 1f. The large-diameter flange 1i.sub.2 of the insulating seat 1i is located between the two hair springs 1g and 1j to prevent their contact.
A second lead terminal 4d of the light emitting diode 4c is electrically connected to a conducting pattern (not shown) on the underside of the printed circuit card 4b, with which one end of a metal coil spring 6 is kept in contact. The coil spring 6 is installed compressed between the underside of the printed circuit card 4b and a spring retainer cup 5 made of conductive material, which is mounted on the outer circumference of the insulating seat 1i and contacts the connector block 1k. The spring retainer cup 5 has a side wall 5.sub.i slightly larger in inner diameter than the outer diameter of the coil spring 6 so as to stably receive the coil spring 6 for secure electric connection and to prevent it from coming into contact with other parts.
Mounted on the base portion of the pointer 4 is a pointer cap 4f which covers a light introducing portion 4c.sub.1 of the indicating portion 4a, the light emitting diode 4c and the printed circuit card 4b, blocking them from external view.
Denoted 1l are terminals to which input signals for driving the drive unit I are supplied.
In the above construction, the first lead terminal 4d of the light emitting diode 4c is connected to the first terminal 1e through the conducting pattern on the upper surface of the printed circuit card 4b, pointer collar 4e, pointer shaft 1a, connector block 1h and hair spring 1g. The second lead terminal 4d is connected to the second terminal 1f through the conducting pattern on the underside of the printed circuit card 4b, coil spring 6, spring retainer cup 5, connector block 1k and hair spring 1j.
When a power source is connected between the first and second terminals 1e, 1f, current flows through the light emitting diode 4c to illuminate it. Light emitted by the light emitting diode 4c is directly introduced from the light introducing portion 4c.sub.1 into the indicating portion 4a where it is scattered by the diffused reflection surface at the underside 4a.sub.1 so that the entire indicating portion 4a lights up with a uniform brightness.
The two hair springs 1g, 1j are wound in opposite directions so that, with the pointer 4 set at the zero position on the face plate 2, the torque of the hair spring 1g and the torque of the hair spring 1j oppose and offset each other to provide only enough restraining torque to the pointer shaft 1a.
The automotive meter of the above construction is assembled as follows. The drive unit 1, which was already assembled with the connector block 1h, hair spring 1g, insulating seat 1iconnector block 1k, hair spring 1j and spring retainer cup 5, is mounted to the light conducting member 3. Then the coil spring 6 is installed through the openings 2a, 3a. The preassembled pointer collar 4e of the pointer 4 is fitted under pressure into the through-hole 1i.sub.1 of the insulating seat 1j, followed by the end of the pointer shaft 1a being pressed into the through-hole 4e.sub.1 of the pointer collar 4e. Now, the coil spring 6 is compressed between the printed circuit card 4b and the spring retainer cup 5 to achieve a desired electrical connection.
In the aforementioned prior art automotive meter, the pointer 4 incorporates a large number of members not directly related to the meter function just to supply electric power to the light emitting diode 4c in the self-illuminating pointer 4 without adversely affecting the pointer driving operation. The large number of components poses many problems such as reducing the assembly efficiency, electric conductivity and economy and degrading the balance of the pointer.